1. Field of the Invention
The present invention relates to free-flowing, unpressurized irrigation systems such as corrugated row crop fields, flood irrigation and like systems, and more particularly, to an apparatus and method for providing an equal distribution of water from gated pipe over a field having a gradient.
2. Description of the Prior Art
The prior art discloses numerous systems for the irrigation of agricultural products. These systems can generally be divided into two classifications: those that rely on a high-pressure source for uniform distribution of water, such as sprinklers of various configurations and types; and those that rely on gravity for the uniform distribution of water over a field, such as ditches, flood irrigation and gated pipe. The present invention relates to irrigation systems of the latter type wherein gravity distribution is desired.
A substantial portion of the irrigated farm ground in the United States derives its water supply from centralized community, local or governmental water projects. Each of such projects typically deliver water by gravity flow through a series of open ditches from the central project to the various agricultural lands served by the project. Many systems have been in place for decades and the agricultural lands receiving such waters have had a substantial period of experience to develop methods of distributing the water from the gravity flow open ditch system to the particular cropland concerned.
One of the variables which farmers relying on the above gravity flow systems for irrigation have had to contend with is the variation in flow of water to each particular agricultural property. Typically there are numerous upstream water users to any particular agricultural property. Although control of the flow to each property may be regulated through some third party such as a water master who attempts to maintain the appropriate flow to each user, each agricultural user acts relatively independently in determining the amount of water to be used at any particular time. This can result in a great variation in the flow to any downstream user.
To minimize the fluctuation in water flows and levels, and also to provide water to the largest number of acres possible from the particular project, users are generally required to rotate their irrigation waters throughout each parcel of property. Allocation of water is, therefore, generally premised on 24-hour use by each user and it may take a particular user between and 5 and 14 days to provide water to all portions of any particular parcel. Rotation may be done on a daily basis or on a 12-hour basis or on such other periodic basis as the user determines is best for the particular crop involved. Such rotation will continue throughout the irrigation season.
As is well appreciated by those skilled in the art, any irrigation system using gravity-supplied waters must be capable of metering precise amounts of water to the cropland despite the potential of substantial fluctuations in flow and level of water delivered to the user due to the activities of upstream and downstream users beyond any particular users' control. One system which has gained widespread acceptance for the irrigation of high-quality farm ground is the use of siphon tubes. Each field is worked to provide a relatively flat service with a gradient from the top of the field to the bottom of the field. A ditch is then placed along the top of the field which waters from the central system are diverted into. Small siphon tubes are then set from the ditch at the top of the field to small "corrugations" or ditches which run between rows of crops. One particular field may have 100 or more corrugations, each which must receive water on a periodic basis for irrigation of the crop. The farmer will typically set a number of siphon tubes and than on a periodic basis, remove such tubes and reset them to provide water to different corrugations, continuing such procedure until the complete field is irrigated.
The advantage of the siphon tube method is that variations in the flow and height of head ditch will provide a minimum fluctuation in the water metered through the siphon tubes. The diameter of the siphon tube will largely determine the flow of water into the corrugation. Another advantage of the siphon tube method is that the flow from the siphon tubes is at a very low pressure and thereby minimizes erosion of the corrugates and adjacent planted rows. A further advantage of the overall system is that it does not require the high capital investment of pressurized systems such as pumps, underground pipes and above-ground sprinkler systems, all of which have a relatively limited useful life. Corrugated irrigation techniques from open ditch delivery systems have been in use for decades and still enjoy widespread use.
The disadvantage to the siphon tube distribution method is that it is relatively labor intensive and also results in high water losses through evaporation and soil losses. Although soil losses with siphon tube distribution systems can be greatly mitigated through the use of concrete ditches, such ditches are costly to construct and maintain. Any cracks must be immediately repaired or they may result in washing out of the soil supporting the ditch and depositing large amounts of moisture under the ditch with attendant heaving and further cracking during winter freezes.
As is well appreciated in the art, a greater emphasis is continuously being placed on conservation of water. This emphasis is due to a number of factors including increased demand for limited supplies. It is only natural that due to such emphasis greater consideration would be given to methods of eliminating open ditches and attendant evaporation and high soil losses. It is also noteworthy that soil losses may vary considerably depending on the type of soil concerned. In some areas, soil losses can be so high as to make open ditches totally impractical. In other areas soil losses may be deemed acceptable by the end user. In all geographical areas and soil conditions it is believed that continued conservation efforts will be required to maximize the use of a limited water supply.
One method minimizing such losses, at a substantially reduced cost over concrete ditches, which has recently gained greater and greater acceptance is the use of gated pipe in place of the open ditch and siphon tubes. Gated pipe consists of pipe having a diameter of between 6" and 12" with a number of adjustable openings on the side to allow the flow of water from the pipe to the farmland. Although examples of gated pipe are illustrated in the prior art as early as 1914 (see U.S. Pat. No. Re. 14,081), such pipe has only recently gained commercial acceptance due to the convenience with which it can be used and the high efficiency of use compared to open ditches. Another important factor in the increased use of gated pipe is that it is compatible with the gravity flow systems which are and have been in existence for decades.
To convert an existing ditch and siphon tube system to dated pipe is relatively simple. As indicated above, water is typically delivered to the agricultural land in open ditches through gravity flow. Instead of directing said water into ditches adjoining the field and withdrawing the water with numerous siphon tubes, the water is instead channeled into gated pipe running along the boarder of the field to be irrigated. The various openings on the gated pipe are placed in registry with the corrugated rows of the field to be irrigated and the openings can then be adjusted for flow.
As is well appreciated and as indicated in U.S. Pat. No. Re. 14,081, page 1, lines 98-102, it is desired that the water flow from gated pipe be at minimum pressure in a steady stream to minimize erosion and to obtain a uniform flow.
Although gated pipe has recently gained greater and greater commercial acceptance, there are certain inherent difficulties which have slowed such acceptance. Due to the fact that once water is channeled into the gated pipe it encounters a closed system, the particular gradient upon which the gated pipe is placed has a substantial effect on the flow of water from the openings. For example, if the gated pipe is placed along a substantial gradient, it would tend to cause water at the lower end to have a greater pressure requiring narrowing the openings to provide a smaller but more forceful stream for an equivalent flow to the upper free flowing end of the pipe. Although it is possible to make such adjustments, it is difficult visually to provide equal flows where the lower end consists of a strong, spray-like stream and the upper end consists of a steady, low-pressure flow. Much of the irrigation work is also done by inexperienced field hands and instruments are not typically available to measure flow such that visual adjustments are the rule. If high pressure is encountered at the lower end of the pipe, the strong stream which results is also detrimental in that it causes erosion of the field and crop.
Various methods have been attempted to solve these problems. The flow of water into the pipe may be restricted such that the flow from the upper end reduces the water level sufficiently that minimum pressure results at the lower end. Attempts have also been made to put valves at various spacings along the pipe to control the flow through the gated pipe such that equal quantities of water will be dispersed from the upper end as the lower end.
In a steady state system, through such valves and precise adjustment to the gates, equal flows may be achieved, although it does require substantial experimentation and adjustments to achieve equal flow throughout the pipe on a gradient. As is well appreciated in the art and as indicated above, the typical user does not encounter a steady state system. There may be increased levels and flows to the end user or decreased flows. Therefore, even once an acceptable steady state system is achieved, upon the farmer going home and leaving the system over night, changes in the volume of water supplied to the user due to third-party practices, are beyond the users control and may result in the system being thrown out of balance resulting in uneven irrigation to the field.
Another problem encountered in the use of valves to control the flow in gated pipe is the substantial waste water and trash encountered by many users in their irrigation water. This results in part from the fact that downstream users almost assuredly are receiving water which to a large degree has been already circulated through fields by one or more upstream users. It is calculated that the water received by many users has already been used between three and six times before it is returned to the river or final waste ditch. Even extremely small amounts of trash can result in the partial plugging of gates throwing such systems out of balance.
Another substantial disadvantage to the use of valves in metering flow from gated pipe is the difficulty encountered should adjustments to the flow be later desired. For example, once the user goes through the various steps to adjust the flow correctly over the complete length of the gated pipe for existing conditions, should the user decide that additional flow is desired from the upper portion of the pipe it would require readjustment of the various valves and numerous gates. Likewise, upon each rotation of water, the complete balancing of the system would again be required. As is well appreciated by those skilled in the art, in a closed system, every significant change in flow from an upstream gate will reduce the water available downstream and require readjustment of the system. Even under ideal conditions, the balancing of a system of gated pipe through the use of valves is a time consuming operation which requires numerous adjustments of the various gates and valves on a trial and error basis as each adjustment effects the other adjustments.
It is a principal object of the present invention to provide a method and apparatus to allow easy and convenient adjustment of the flow of water from gated pipe which is relatively impervious to changes in the volume of water supplied and the trash typically encountered.
It is a further object of the present invention to make the use of gated pipe much more convenient and commercially acceptable.
It is a further object of the present invention to provide the minimum head desired with gated pipe throughout the length of the pipe despite substantial gradients and variations in flow.
It is the further object of the present invention to allow farmers great flexibility in irrigation rotation such that water from a single length of gated pipe may be drawn from the upper and lower ends simultaneously with substantially equal flows and low pressure, and rotation to other portions of the pipe can be made without further adjustments.
It is the further object of the present invention to eliminate the need for precise control of the flow of water into gated pipe from the open gravity ditches.
It is another object of the present invention to eliminate the need for the precise adjustment of various valves in gated pipe.